This invention relates to adjustable end wrenches having a fixed jaw and an adjustable jaw cooperating with the fixed jaw, and including means for releasably locking the adjustable jaw in fixed, object gripping, position. The invention is particularly useful with end wrenches of the worm gear-rack mechanism type.
Wrenches of the worm gear-rack mechanism type and a particular problem associated therewith are well known. The following three paragraphs are from the introduction of U.S. Pat. No. 4,375,174, Mar. 1, 1983, the subject matter of which is incorporated herein by reference.
Adjustable, parallel jaw end wrenches with worm gear and rack mechanisms have been in general use for probably a hundred years or more. The advantage of such a wrench obviously resides in its ability to take the place of a set of several non-adjustable end wrenches. The adjustable end wrenches have never been a perfect substitute, however, because they tend to back off the object being gripped, especially when a great amount of torque is applied. A stubborn hex head bolt, for example, will often have its corners rounded due to slippage of an adjustable end wrench as one attempts to turn the bolt. Because of the slippage problem, the adjustable, parallel jaw end wrenches in common use today have come to be known as "knuckle busters."
Many attempts have been made over the years to provide adjustable end wrenches with releasable locking mechanisms to prevent them from backing off once they have been tightened on an object. None of the wrenches equipped with such mechanisms appears to have been commercially successful, however. Evidently they have all suffered from one or more of the following drawbacks: too complicated, and therefore too expensive to manufacture; not strong enough to withstand high bending moments; too massive; or requiring too much structural material to be cut away from the wrench, thereby weakening it more than can be tolerated. I have invented a releasable locking mechanism for such a wrench that does not suffer from any of those drawbacks.
The adjustable end wrench which is improved by my locking mechanism is well known in the art. It is comprised of an elongated handle that ends in a fixed jaw portion having a face for engaging one side of an object to be gripped by the wrench; an undercut slot in the fixed jaw portion, the axis of the slot being substantially perpendicular to the plane of the face of the fixed jaw; a movable jaw member having an elongated, protuberant shank portion that mates with the undercut slot and is slidably held in the slot, a face that is opposed to the face of the fixed jaw, and a rack portion that runs parallel to the axis of the slot; an opening, or "window", through the fixed jaw portion adjacent to the slot, the opening being in communication with the slot; and a worm gear rotatably mounted in the opening in driving engagement with the rack portion of the movable jaw member, so that by turning the worm gear one can adjust the distance between the faces of the fixed and movable jaws.
In U.S. Pat. No. 4,375,174, the means for locking the movable jaw comprises a cam mechanism for pushing the gear, and therefore the rack and movable jaw as well, toward the fixed jaw thereby locking the movable jaw in place. A shortcoming of the patent is that it is somewhat complex and expensive. Also, the pressure on the gear by the cam mechanism is a function of the proper dimensioning of the various parts, thereby requiring relatively small manufacturing tolerances. Further, while applicant has not examined an actual wrench according to this patent, it at least appears from the patent that, while locking of the jaws occurs in a direction from jaw to jaw, not a great deal of additional locking is provided with respect to side to side or rotational movements of the movable jaw.
Other patents known to me are U.S. Pat. Nos. 733,617 (Jul. 14, 1903) and 3,093,019 (Jun. 11, 1963), the subject matter of which are also incorporated herein by reference.
In '617, a movable jaw is included which is slightly pivotable with respect to the wrench shank, and set screws are provided for, in special circumstances, locking the movable jaw against the shank to prevent pivoting movement. The wrench of this patent, however, is significantly different from the type of wrenches with which the present invention is concerned, and it is not clear, even if it should occur to skilled workers to use the set screw of this patent, how the set screws of the patent can be used with wrenches of the type improved by my invention.
Patent '019 shows the use of a threaded stud extending from the movable jaw in a direction perpendicular to the shank and a locking nut mechanism for movement along the length of the stud and into engagement with the shank for locking the movable jaw in position. However, the wrench in this patent is also significantly different from wrenches of the type improved by the present invention and it is not clear how the locking nut mechanism (relatively complicated and expensive) can be incorporated in wrenches of the present type.
Also, in both patents '617 and '019, the movable jaw locking means function merely to lock the movable jaw in place while not changing the jaw clamping pressure. In many instances, increasing the maximum clamping pressure obtainable by rotation of the worm gear by the user is desirable.
Accordingly, a need exists in adjustable end wrenches of the worm gear-rack mechanism type for a means, preferably inexpensive and long lasting, for rigidly locking in place, both longitudinally and angularly, the adjustable jaw of the wrench, as well as increasing the clamping pressure as obtained by rotation of the worm gear.